The present invention relates to a homogeneous EMI shielded vent comprising an electrically conductive frame element and a porous shielding element. The vent structure is formed as a single integrated and homogenous part using a selective laser sintering (SLS) technique. The vent structure of the invention can be formed into a variety of complex shapes and configurations, and does not require the use of solders, conductive adhesives, or mechanical bonding techniques frequently used for fabricating EMI vent panels. Advantageously, the porous shielding element is a honeycomb structure containing interconnected cells providing both adequate ventilation and reliable EMI shielding.
The homogenous EMI shielding vent of the invention is designed to cover a ventilation opening in an electronics housing or other device, and is particularly adapted for use in aircraft and military environments where foreign object debris (“FOD”) is a persistent problem. Foreign object debris is created in current vent panels, which are constructed from a separate frame and filter media, when these separate components are cut and installed.
The vent panel of the invention is a homogenous structure configured to accommodate the flow of cooling air into the enclosure while maintaining electrical continuity and EMI shielding effectiveness across the opening. Since the structure is a one-piece or homogenous part, the use of devices for attaching the separate vent panel elements is eliminated. Such attachment devices include soldering, plating, conductive epoxy coatings, and mechanical attachments which can be incidental rather than permanent attachments. The elimination of these various attachment methods serves to improve the overall performance of the vent, avoid problems due to a failure of attachment devices, and improve corrosion resistance.
In general, the operation of electronic devices such as monitors, radios, computers, medical instruments, business machines, communications equipment, and the like is attended by the generation of electromagnetic radiation within the electronic circuitry of the equipment. As is detailed in U.S. Pat. Nos. 5,202,536; 5,142,101; 5,105,056; 5,028,739; 4,952,448; and 4,857,668, such radiation often develops as a field or as transients within the radio frequency band of the electromagnetic spectrum, i.e., between about 10 KHz and 10 GHz, and is termed “electromagnetic interference” or “EMI”. EMI is known to interfere with the operation of other proximate electronic devices. “EMI” is used herein interchangeably with the term “radio frequency interference” (“RFI”).
For attenuating EMI effects, suitable shielding having the capability of absorbing and/or reflecting EMI energy may be employed both to confine the EMI energy within a source device, and to insulate that device or other “target” devices from other source devices. Such shielding is provided as a barrier which is interposed between the source and the other devices, and most often is configured as an electrically conductive and grounded housing or other enclosure which surrounds the EMI generating circuitry of the source device. However, when such circuitry is contained within the confined space of an enclosure, it often is necessary to provide a cooling or ventilation means to dissipate the heat which is generated by the circuitry. Most enclosures therefore are formed with one or more air intake and/or exhaust openings or ports for natural or forced convective circulation of air between the interior of the enclosure and the ambient environment.
Left uncovered, such openings would represent a discontinuity in the surface and ground conductivity of the enclosure, with the result of a decrease in the EMI shielding effectiveness of the enclosure. Accordingly, shielded vent panels have been used for covering the openings in an manner which allows ventilation of the enclosure while electrical continuity, i.e., grounding, across the vent opening is maintained.
In basic construction, such vent panels, which are sized to span the corresponding opening in the enclosure, conventionally are formed from a sheet of a porous, electrically-conductive shielding media, i.e. a vent opening, and an electrically-conductive frame member configured to support the media by extending about the outer periphery thereof. The vent panels may also be stamped or cast. The media, which may be an expanded metal mesh or, alternatively, a honeycombed-structured or other cellular structured metal foil, is received in or is otherwise attached to the frame, which typically is provided as an extruded aluminum, stainless steel, Monel, or other metal profile. The frame, in turn, may be fastened to the enclosure over the opening thereof with screws or the like, and a compressible, electrically-conductive seal or gasket optionally provided for improved electrical contact between the frame and the enclosure.
However, for electrical continuity to be maintained across the opening, good electrical contact must be provided not only between the frame and the enclosure, but also between the media and the frame. In this regard, conventional panels may employ a C-shaped frame channel or other extrusion including a V-shaped or other projection or edge integrally formed within one of the sides of the channel. With the periphery of the media being received within the channel, the sides thereof are compressed to cause the projection or edge to penetrate into the media and thereby establish good electrical contact. Vent panels of such type are marketed commercially by the Chomerics Division of the Parker-Hannifin Corp. under the tradenames “Cho-Cell™”, “Shield Cell®”, “Omni Cell®”, “Slimvent™”, and “Streamshield™”. Alternatively, the media may be fit into the frame and then bonded thereto using a conventional joining technique such as resistance welding, brazing, soldering, or the like. Vent panels of this type are also marketed commercially by the Chomerics Division of Parker-Hannifin Corp.
EMI shielding vents are also described in the following patents: U.S. Pat. Nos. 6,426,459; 6,362,417; and 6,211,458; 5,032,689; 6,710,241; 7,038,124; and 7,575,708. Other vents and materials therefore are described in U.S. Pat. Nos. 3,546,359; 3,580,981; 3,553,343; 3,584,134; 3,821,463; 4,616,101; 4,249,033; 4,616,101; 5,007,946; 5,401,914; 5,895,885; and 5,910,639, JP 8064988, and WO 97/32459.
In view of the proliferation of electronic devices, it is to be expected that continued improvements in EMI shielded vent panels would be well-received by industry, and particularly by the designers of enclosures for personal computers, file servers, telecommunication equipment, and similar systems which now operate at frequencies of 500 MHz or more. Indeed, as the processing speeds of electronic devices continue to increase with the attendant generation of higher frequency EMI radiation and greater heat output, enclosure designers are faced with the seemingly competing requirements of providing both adequate ventilation and effective EMI shielding. In such applications, a honeycomb shielding media, such as is disclosed in U.S. Pat. Nos. 3,821,463; 5,895,885; 5,910,639, often may be preferred over other media as it is known to provide effective EMI shielding at higher frequencies with less restriction to air flow. Moreover, certain applications may specify a cast or similar-type frame construction which, in contrast to an extrusion, may be formed without corner seams and, as a result, may be made more structurally rigid and may be formed into more complex shapes. Ultimately, a preferred vent construction would be economical to manufacture, and would exhibit both reliable EMI shielding performance and good ventilation even in high frequency applications.
Ideally, the EMI vent panel would be fabricated from a single metal structure to form a homogenous part which would avoid the above complications associated with the joining of separate media and frame elements. This type of fabrication has not heretofore been possible due to issues of cost and fabrication technique limitations.
Recently, several fabrication techniques have been proposed for use in the manufacture of complex metal parts and structures. See, for instance, U.S. Pat. No. 7,575,708, which describes a process for manufacturing aerospace parts from a powdered nylon material using a selective laser sintering technique.
It will be appreciated that it would be of considerable advantage to develop an improved vent panel which exhibits reliable EMI shielding and air flow characteristics, which is economical to manufacture, which has structural integrity, and which ideally would be a one-piece homogenous construction. These and other advantages will be readily apparent to those skilled in the art based upon the disclosure contained herein.
The disclosure of each of the patents set forth above is incorporated by reference herein in their entirety.